Recently, we introduced an approach for more easily interpreting searches for resonances at the LHC-and to aid in distinguishing between realistic and unrealistic alternatives for potential signals. ...This “simplified limits” approach was derived using the narrow width approximation (NWA)-and therefore was not obviously relevant in the case of wider resonances. Here, we broaden the scope of the analysis. First, we explicitly generalize the formalism to encompass resonances of finite width. We then examine how the width of the resonance modifies bounds on new resonances that are extracted from LHC searches. Second, we demonstrate, using a wide variety of cases, with different incoming partons, resonance properties, and decay signatures, that the limits derived in the NWA yield pertinant, and somewhat conservative (less stringent) bounds on the model parameters. We conclude that the original simplified limits approach is useful in the early stages of evaluating and interpreting new collider data and that the generalized approach is a valuable further aid when evidence points toward a broader resonance.
Simplified Limits on New LHC Resonances Simmons, Elizabeth H.; Chivukula, R. Sekhar; Ittisamai, Pawin ...
EPJ Web of Conferences,
01/2017, Letnik:
137
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
If an excess potentially heralding new physics is noticed in collider data, it would be useful to be able to compare the data with entire classes of models at once. This talk discusses a method that ...applies when the new physics corresponds to the production and decay of a single, relatively narrow, s-channel resonance. A simplifed model of the resonance allows us to convert an estimated signal cross section into model-independent bounds on the product of the branching ratios corresponding to production and decay. This quickly reveals whether a given class of models could possibly produce a signal of the observed size. We will describe how to apply our analysis framework to cases of current experimental interest, including resonances decaying to dibosons, diphotons, dileptons, or dijets.
As we amass more LHC data, we continue to search for new and improved methods of visualizing search results, in ways that are as model independent as possible. The simplified limits framework is an ...approach developed to recast limits on searches for narrow resonances in terms of products of branching ratios (BRs) corresponding to the resonance's production and decay modes. In this work, we extend the simplified limits framework to a multidimensional parameter space of BRs, which can be used to unfold an ambiguity in the simplified parameter ζ introduced when more than one channel contributes to the production of the resonance. It is also naturally applicable to combining constraints from experimental searches with different observed final states. Constraints can be visualized in a three-dimensional space of branching ratios by employing ternary diagrams, triangle plots which utilize the inherent unitarity of the sum of the resonance's BRs. To demonstrate this new methodology, we recast constraints from recent ATLAS searches in diboson final states for spin-0, -1, and -2 narrow resonances into constraints on the resonance's width-to-mass ratio and display them in the space of relevant branching ratios. We also demonstrate how to generalize the method to cases where more than three branching ratios are relevant by using N -simplex diagrams, and we suggest a broader application of the general method to digital datasets.
Simplified limits on resonances at the LHC Chivukula, R. Sekhar; Ittisamai, Pawin; Mohan, Kirtimaan ...
Physical review. D,
11/2016, Letnik:
94, Številka:
9
Journal Article
Recenzirano
Odprti dostop
In the earliest stages of evaluating new collider data, especially if a small excess may be present, it would be useful to have a method for comparing the data with entire classes of models, to get ...an immediate sense of which classes could conceivably be relevant. In this paper, we propose a method that applies when the new physics invoked to explain the excess corresponds to the production and decay of a single, relatively narrow, s-channel resonance. A simplifed model of the resonance allows us to convert an estimated signal cross section into general bounds on the product of the branching ratios corresponding to the dominant production and decay modes. This quickly reveals whether a given class of models could possibly produce a signal of the required size at the LHC. Our work sets up a general framework, outlines how it operates for resonances with different numbers of production and decay modes, and analyzes cases of current experimental interest, including resonances decaying to dibosons, diphotons, dileptons, or dijets. If the LHC experiments were to report their searches for new resonances beyond the standard model in the simplified limits variable ζ defined in this paper, that would make it far easier to avoid blind alleys and home in on the most likely candidate models to explain any observed excesses.
Discovering strong top dynamics at the LHC Chivukula, R. Sekhar; Ittisamai, Pawin; Simmons, Elizabeth H. ...
Physical review. D, Particles, fields, gravitation, and cosmology,
11/2012, Letnik:
86, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We analyze the phenomenology of the top-pion and top-Higgs states in models with strong top dynamics, and translate the present LHC searches for the Standard Model Higgs into bounds on these scalar ...states. We explore the possibility that the new state at a mass of approximately 125 GeV observed at the LHC is consistent with a neutral pseudoscalar top-pion state. We demonstrate that a neutral pseudoscalar top pion can generate the diphoton signal at the observed rate. However, the region of model parameter space where this is the case does not correspond to classic top-color-assisted technicolor scenarios with degenerate charged and neutral top pions and a top-Higgs mass of order 2mt; rather, additional isospin violation would need to be present and the top dynamics would be more akin to that in top seesaw models. Moreover, the interpretation of the new state as a top pion can be sustained only if the ZZ (four-lepton) and WW (two-lepton plus missing energy) signatures initially observed at the 3sigma level decline in significance as additional data are accrued.
The limitations of the Standard Model of particle physics, despite its being a well-established theory, have prompted various proposals for new physics capable of addressing its shortcomings. The ...particular issue to be explored here is the mechanism of electroweak symmetry breaking, the probing of which lies within the TeV-scale physics accessible to the Large Hadron Collider (LHC). This thesis focuses on the phenomenology of a class of models featuring a dynamical breaking of the electroweak symmetry via strong dynamics. Consequences of recent experiments and aspects of near-future experiments are presented. We study the implications of the LHC Higgs searches available at the time the related journal article was written for technicolor models that feature colored technifermions. Then we discuss the properties of a technicolor model featuring strong-top dynamics that is viable for explaining the recently discovered boson of mass 126 GeV. We introduce a novel method of characterizing the color structure of a new massive vector boson, often predicted in various new physics models, using information that will be promptly available if it is discovered in the near-future experiments at the LHC. We generalize the idea for more realistic models where a vector boson has flavor non-universal couplings to quarks. Finally, we discuss the possibilities of probing the chiral structure of a new color-octet vector boson.
We have studied neutrino phenomenology in the supersymmetric type-I seesaw
model endowed with the $\Gamma_2 \simeq S_3$ modular symmetry. We have
identified different realizations of the $S_3$ ...modular symmetry, referred to as
models A, B, C, and D. The 4 models are compatible with neutrino mass being
inverted ordering (IO). Moreover, models A, B, and D can also accommodate
normal ordering (NO) neutrino masses. We identify parameter space for each
model compatible with neutrino oscillation at the 2-$\sigma$ level. We then
proceed to study the neutrino phenomenology of each model. We find that the
lightest neutrino mass can be as light as 0.64 meV in the case of NO in model A
and 50 meV in the case of IO in model D. The smallest effective electron
neutrino mass attainable in our analysis is 8.8 meV in the case of NO (model
A), and 50 meV for IO (model D). Finally, we note that the effective Majorana
mass can be as small as 0.33 meV in the case of NO (model A) and 22 meV for IO
(model D).
We have studied neutrino phenomenology in the supersymmetric type-I seesaw model endowed with the \(\Gamma_2 \simeq S_3\) modular symmetry. We have identified different realizations of the \(S_3\) ...modular symmetry, referred to as models A, B, C, and D. The 4 models are compatible with neutrino mass being inverted ordering (IO). Moreover, models A, B, and D can also accommodate normal ordering (NO) neutrino masses. We identify parameter space for each model compatible with neutrino oscillation at the 2-\(\sigma\) level. We then proceed to study the neutrino phenomenology of each model. We find that the lightest neutrino mass can be as light as 0.64 meV in the case of NO in model A and 50 meV in the case of IO in model D. The smallest effective electron neutrino mass attainable in our analysis is 8.8 meV in the case of NO (model A), and 50 meV for IO (model D). Finally, we note that the effective Majorana mass can be as small as 0.33 meV in the case of NO (model A) and 22 meV for IO (model D).
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